[PATCH v24 32/34] ALSA: usb-audio: Check for support for requested audio format

[Wesley Cheng]

Allow for checks on a specific USB audio device to see if a requested PCM
format is supported.  This is needed for support when playback is
initiated by the ASoC USB backend path.

Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
---
 sound/usb/card.c | 31 +++++++++++++++++++++++++++++++
 sound/usb/card.h |  2 ++
 2 files changed, 33 insertions(+)

diff --git a/sound/usb/card.c b/sound/usb/card.c
index 70b7f22ff495..8c22f6bfdef2 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -176,6 +176,37 @@ void snd_usb_rediscover_devices(void)
 }
 EXPORT_SYMBOL_GPL(snd_usb_rediscover_devices);
 
+/*
+ * Checks to see if requested audio profile, i.e sample rate, # of
+ * channels, etc... is supported by the substream associated to the
+ * USB audio device.
+ */
+struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
+			struct snd_pcm_hw_params *params, int direction)
+{
+	struct snd_usb_audio *chip;
+	struct snd_usb_substream *subs;
+	struct snd_usb_stream *as;
+
+	/*
+	 * Register mutex is held when populating and clearing usb_chip
+	 * array.
+	 */
+	guard(mutex)(&register_mutex);
+	chip = usb_chip[card_idx];
+
+	if (chip && enable[card_idx]) {
+		list_for_each_entry(as, &chip->pcm_list, list) {
+			subs = &as->substream[direction];
+			if (snd_usb_find_substream_format(subs, params))
+				return as;
+		}
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(snd_usb_find_suppported_substream);
+
 /*
  * disconnect streams
  * called from usb_audio_disconnect()
diff --git a/sound/usb/card.h b/sound/usb/card.h
index f0794aa06cd7..99d6a784eacf 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -220,4 +220,6 @@ int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops);
 int snd_usb_unregister_platform_ops(void);
 
 void snd_usb_rediscover_devices(void);
+struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
+				struct snd_pcm_hw_params *params, int direction);
 #endif /* __USBAUDIO_CARD_H */